On 6/15/05, ronggui <0034058 at fudan.edu.cn>
wrote:> gg <- function(y) {
> ggg <- function() {
> cat("current frame is", sys.nframe(), "\n")
> cat("parents are", sys.parents(), "\n")
> print(sys.function(0)) # ggg
> print(sys.function(2)) # gg
> }
> if(y > 0) gg(y-1) else ggg()
> }
>
>
> > gg(3)
> current frame is 5
> parents are 0 1 2 3 4
> function() {
> cat("current frame is", sys.nframe(), "\n")
> cat("parents are", sys.parents(), "\n")
> print(sys.function(0)) # ggg
> print(sys.function(2)) # gg
> }
> <environment: 071C62FC>
> function(y) {
> ggg <- function() {
> cat("current frame is", sys.nframe(), "\n")
> cat("parents are", sys.parents(), "\n")
> print(sys.function(0)) # ggg
> print(sys.function(2)) # gg
> }
> if(y > 0) gg(y-1) else ggg()
> }
>
>
> my question is ,why the current frame is 5?why the sys.function is ggg.i am
quite confused.
> anyone can give me some clue?i have read the ?sys.parent,but i still can
not get the point exactly.
We start out at frame 0 and then:
1. we call gg(3) so now we are at frame 1
2. which calls gg(2) so now we are at frame 2
3. which calls gg(1) so now we are at frame 3
4. which calls gg(0) so now we are at frame 4
5. which calls ggg() so now we are at frame 5
sys.function(0) seems to be referring to the current frame
(not frame 0 as the which= documentation in ?sys.function
seems to imply). Since sys.function(0) is called within ggg
we get the result. Also sys.function(2) refers to frame 2
and referring to the numbered list above we see it is gg.